1. Field of the Invention
The present invention relates generally to drive systems for mobile power equipment, and more particulraly to draw works for driving the cable of mobile power cranes.
2. Relevant Background
Early forms of mobile power driven machinery or equipment, such as cranes and power shovels, utilized drive systems or draw works in which the shaft was coupled to a wheel driven by a belt about the engine pulley of the power unit. An example of such an arrangement is shown and described in U.S. Pat. No. 2,380,626 to Zeilman et al. The draw works in the portion of the power equipment employed to feed or reverse a cable used for lifting or lowering operations. In a crane, of course, the cable and associated hook or other retention means usually serves to lift and lower heavy or bulky construction materials from one location to another at the job site. In a power shovel, the cable may be used to operate the shovel portion itself.
The prior art belt driven systems were notorious for power transfer problems caused by belt slippage or creepage. Belt slippage resulted in seriously inefficient power transfer from the engine pulley to the shaft of the gear train used to drive the cable. Moreover, the slippage probelm resulted in overheating of the belt itself, and ultimately in the rupture of the belt if the equipment were used continuously for even relatively short periods of time. Overheating of the engine was also a probelm because of the inefficient power transfer. Accordingly, it was necessary to shut down the equipment at regular intervals to allow the components to cool down, but even that measure was inadequate to prevent relatively frequent breakdowns.
In an effort to alleviate the slippage problem in some types of belt driven machinery, idler pulleys, some of which were vibrating or adjustable, were used to force the belt into a greater degree of engagement with the main drive pulley. An example of such an arrangement is described in U.S. Pat. No. 1,570,591 to Mercer. However, these techniques in and of themselves were not successful where heavy equipment such as a crane draw works was involved. In fact in many cases it was found that increasing the tension on the belt, coupled with continuing creepage, caused the belt to snap.
Partly as a result of these problems the equipment manufacturers moved away from belt driven systems, and ultimately to the use of chains as the standard for draw works in cranes. An example of the chain drive system is shown in U.S. Pat. No. 2,248,326 to Baker, which describes a cable operated excavating shovel. However, although the use of chain driven draw works has eliminated some of the problems that had been encountered with prior art belt driven systems, the chain driven units are not without their own set of problems.
For example, chain drives require constant lubrication, particularly where used for relatively large draw works intended for long periods of continual operation. Typically, lubrication is supplied by running the chain through a lubricant case or crankcase positioned between the sprocket wheels about which the chain is wrapped. The lubricating system including the case and the associated lubricating pump must undergo regular routine maintenance to assure smooth running operation of the pump and an absence of leaks in the crankcase. Failure to perform such maintenance and to repair or replace faulty components will result in inadequate or a complete absence of the required lubrication, and ultimately, in chain burnout.
Burnout is a serious problem encountered all to often in chain driven draw works, and since it occurs while the equipment is in use, it means the equipment will be down all or part of a day at the job site, where the environmental conditions for ill-suited for repair or replacement. Alternatively, the equipment must be loaded on a flat bed trailer for return to the storage or maintenance yard where repair or replacement is most efficiently performed. To a contractor, equipment down time is often the largest single factor in delays or failure to timely complete the work, and the difference between a profit or loss on the job.
It is a principal object of the present invention to provide an improved drive system for mobile power equipment draw works, and especially for mobile crane draw works.